This application relates to and incorporates herein by reference Japanese Patent Application No. 10-365962 filed on Dec. 24, 1998.
1. Field of the Invention
The present invention relates to a method of injection-molding coil spools for ignition coil devices, and particularly to a method of injection-molding a spool of a primary coil of a stick-type ignition coil device.
2. Related Art
Generally, a stick-type ignition coil device for engines includes a column-shaped central core, a primary spool disposed coaxially with the core, a primary coil wound around the primary spool, a secondary spool disposed coaxially with the core and disposed radially inside the primary spool, and a secondary coil wound around the secondary spool.
Since the stick-type ignition coil device is installed in a plug hole of each cylinder of an internal combustion engine, an outer diameter of the stick-type ignition coil device should not be greater than an inner diameter of the plug hole. Therefore, the spools are preferably thinned and elongated in order to ensure winding space of the coils.
The spools are formed by injection-molding a resin. However, this necessitates an insulation tape around the thinned winding portion of the primary spool in order to ensure the dielectric withstanding voltage, because the primary spool is located between the primary coil and the secondary coil.
The present invention has an object to provide a method of injection-molding a coil spool of an ignition coil device, which can ensure an adequate dielectric withstanding voltage without requiring an insulation tape around the coil spool thereby to reduce production costs.
According to the present invention, a coil spool of an ignition coil device is formed by molding a resin in a cavity of a molding die. A gate of the molding die is arranged at a part where a portion other than a coil winding portion is to be formed. An insulating resin is injected through the gate to form the coil spool. The coil spool and the coil are for a primary unit of the ignition coil device, and disposed radially outside of a secondary unit of the ignition coil device.
Preferably, the gate is a side-type and arranged at a part where each flange is to be formed on the coil spool. Alternatively or in combination, the gate is arranged to open in a circumferential direction in a ring shape at a part where a cylindrical part of the coil spool which is outside the flanges in an axial direction is to be formed. Further, alternatively or in combination, the gate is arranged at an axial end of the coil spool and extends in an axial direction.